Electrostatic printing apparatus

ABSTRACT

The printing apparatus has a new type of cathode ray tube which utilizes electrostatic charge deposition. The tube contains a single continuous dielectric plate which forms its face plate. Charges are deposited only on a portion of the dielectric plate where the electron beam strikes and then transferred through the air gap from the dielectric plate to paper by a means of discharge caused by potential difference across the air gap.

United States Patent Tagawa June 27, 1972 [54] ELECTROSTATIC PRINTINGAPPARATUS inventor: Takao Tagawa, Osaka, Japan Assignee: SharpKabushiiti Kaisha, Osaka, Japan Filed: July 29, 1970 Appl. No.: 59,196

Foreign Application Priority Data Aug. l, 1969 Japan ..44/6l809 U.S. Cl...346/74 CR, l78/6.6 A, 346/74 ES Int. Cl ..G03g 15/00, H04n l/30 Fieldof Search .346/74 CR, 74 ES, 74 ESX;

[56] References Cited UNITED STATES PATENTS 3,001,849 9/196] Walkup..346/74 CR Primary Examiner-Howard W. Britton Attorney-Flehr, Hohbach,Test, Albn'tton & Herbert [57] ABSTRACT The printing apparatus has a newtype of cathode ray tube which utilizes electrostatic charge deposition.The tube contains a singlecontinuous dielectric plate which forms itsface plate. Charges are deposited only on a portion of the dielectricplate where the electron beam strikes and then transferred through theair gap from the dielectric plate to paper by a means of dischargecausedby potential diflerence across the air gap.

6 Clains, 8 Drawing Figures PATENTEIJJuIm I972 SHEET 10F 3 I *l'I'I ISECONDARY EMISSION RATIO ELECTRON ENERGY (v INVENTOR. TAKAO TAGAWA BY3%, m 'a/ W ATTORNEYS PATENTEDmzv 1972 saw 2 or 3 1 zs IIIII1!AIWII% 2425 v 23 VOLTS DISCHARGE VOLTAGE (v) I l O 20 30 MICRONS INTERVAL (t) Ik\\\ & 32 1 V///// 24 L\\\\\\\ x\\\ t 24 23 E FIG 6 23 25 I INVENTOR. F/5 BY TAKAO TAGAWA WWW ATTORNEYS PATENTEDJUMN I972 3,673,599 SHEEI 3 OF 3TAKAO TAGAWA ATTORNEYS INVENTOR.

ELECTROSTATIC PRINTING APPARATUS BACKGROUND OF THE INVENTION Thisinvention relates to an'electrostatic printing apparatus, and moreparticularly to an improved apparatus including a cathode ray tube whichutilizes electrostatic charge deposition.

Several methods for depositing charge patterns at high speed have beendeveloped. Perhaps the simplest method is to utilize electrostaticcharge deposition. These developments depend greatly on the appearanceof a new type printing cathode ray tube. The cathode ray tube, socalledpin-tube has a face plate penetrated by an array of many fine pinelectrodes. The printing tube beam is density-modulated by the signaland scans the inner ends of the pin electrodes in the tube. The latentcharge pattern is formedon the recording paper moving in the front ofouter ends of the pin electrodes. The tube permits rapid recording,because horizontal scanning is achieved by the electron beam.

The printing tube is therefore being used in high speed facsimileequipment, in phototelegraphy equipment, in oscilloscope output printersand in computer Output printers.

The tube has further wide application in systems where high speed,remote print-out or local reproduction of copy is required.

However, the printing tubes of the above type suffers from variousdisadvantages. A single row of close-spaced fine pins must be embeddedinto the face plate with high accuracy and furthermore the individualpins in the tube face must be electrically isolated by the embeddingmedium. Such a pin head is expensive because of difficulty inmanufacturing. For exam ple, about 2,000 pins each having a diameter ofabout 25 microns must be positioned on the tube face at interval ofabout I microns.

A capacitive exists unavoidably between two conducting pins or between apin and ground. Because of capacitive coupling charges on one pin aretransferred to a neighboring pin and thus interference occurs in thecharge pattern. The voltage on the pin is represented by V=Q/C (where;Q: charge on pin, C: capacitance of pin) and therefore in order toimprove the sensitivity for recording the quantity of charge should belarge and the value of capacitance small. On account of the parasiticcapacitance the quantity of charge should be larger than theconventional case. The electron beam is used asa high-speed switchingelement to charge selected pins of a close-spaced pin array. The aboveparastic capacitance reduces the speed of switching. In addition, theresolution of the printing tube is poor since charge patterns arediscontinuous due to the discontinuous form of the pin head. It is alsodifficult to design the electron gun in such a way that the electronbeam may equally strike all of the discontinuous pin array.

OBJECTS AND SUMMARY OF THE INVENTION Accordingly, the primary object ofthis invention is to provide an improved electrostatic printingapparatus which avoids one or more of the disadvantages and limitationsof the above conventional apparatus.

Another object of this invention is to provide an electrostatic printingapparatus having the simplest tube construction.

Still another object of this invention is to provide an electrostaticprinting apparatus wherein the tube target has a continuous form.

A further object of this invention is to provide an electrostaticprinting apparatus in which the printing tube possesses a continuoustarget member not having the parasitic capacitors.

It is still a further object of this invention to provide anelectrostatic printing apparatus which has a good resolution and a highspeed of switching.

Another object of this invention is to provide an electrostatic printingapparatus in which the quantity of charge required is reduced. Anadditional object of this invention is to provide an electrostaticprinting apparatus in which the electron beam scanning can be achievedwith ease.

In summary, this invention refers primarily to improved electrostaticprinting apparatus which comprises a cathode ray tube including anelectron gun, an electron scanning means and a continuous target memberwhich is composed of a single dielectric material, the continuous targetbeing scanned by electrons from the electron gun so that charge isdeposited only on a portion of the target where the electron beamstrikes, a dielectric recording sheet running in the front of thecontinuous target, and a gaseous gap between the continuous target andthe recording sheet, through which the charge patterns on the continuoustarget are transferred to the recording sheet by means of discharge.

In order to achieve these objects, the apparatus of this invention usesa single continuous dielectric plate as a target instead of theconventional array of conducting pins. The electrostatic chargedeposition of this invention is therefore accomplished by an uniquemechanism differing from the case of using conducting pins. In apparatusof this invention, charge caused by electron impact is deposited only ona portion of the inner surface of the target plate, and is not conductedto the outer surface. A potential on the charged target portion becomesnegative (or positive) so that it produces a potential difference acrossthe gaseous gap. When such potential difference is greater than thedischarge voltage, discharge takes place across the gaseous gap.Negative (or positive) charge produced by discharge attaches to thedielectric sheet of the recording paper. Thus, the gaseous gap isessential to a charge transport mechanism in this invention apparatus.It should be noted that the use of the dielectric target obviates theneed of isolation bet ween the individual pins and prevents parasiticcapacitance.

Further details will be apparent from the following explanation ofexamples of embodiments of this invention with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view ofthe electrostatic printing apparatus and its operation connection inaccordance with this invention.

FIG. 2 is a graph showing a characteristic curve'of secondary-emissionratio N to electron energy Ve reaching the target in the printing tube.

FIG. 3 is an enlarged sectional view showing the relative positionrelationship between the target surface and the recording paper in theprinting tube.

FIG. 4 is a graph showing a characteristic curve of the dischargevoltage V to the distance r in the printing tube.

FIG. 5 is an enlarged sectional view showing an improvement of thisinvention.

FIG. 6 is an enlarged sectional view showing another improvement.

FIG. 7 is a schematic diagram showing the whole printing systemincluding a developing and a fixing means.

FIG. 8 is a schematic diagram showing a variation of that shown in FIG.7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A cathode ray tube 10 fordepositing latent electrostatic images on the recording paper isschematically shown in FIG. 1. As in a conventional cathode ray tube,the printing cathode ray tube 10 has in its neck an electron gun thatdirects a focused beam of electrons onto a face plate at the oppositeend of the tube. As is commonly known, the electron gun contains cathode11, control grid 12, screen grid 13 and focusing electrode 14. The anode15 is coated with conducting material called aquadag coating. Thecathode 11 for emitting the electron beam is placed at one end of thetube and it holds a negative potential with respect to the anode 15.

The intensity of the beam is modulated in response to signals such asvideo signals and computer output signals, which are applied to thecontrol grid 12. First biasing source 16 is connected between thecathode l1 and the control grid 12 so that the control grid 12 is morenegative than the cathode 11. The printing input signal from the source17 may be applied to either the control grid 12 or the cathode 11. Thescreen grid 13 connected with the second biasing source 18, is severalhundred volts more positive than the cathode 11 and thus serves toaccelerate electrons emitted from the cathode 11. The potential of thefocusing electrode 14 is held at a potential more positive than thecathode 11 which is of sufficient value to focus the accelerated beam bymeans of third biasing source 19.

A pair of electrostatic deflection plates 20 are placed around the pathof the electron beam and serve to sweep the beam over the face plate,thereby causing the beam to trace on the face plate. Differing from theconventional tube, it provides only horizontal deflection for theelectron beam. The pair of electrostatic deflection plates are, ofcourse, connected to a saw-toothed potential generator not shown. Aknown blanking circuit is attached to the generator. The deflectionmeans may be either electrostatic deflection plates or electromagneticdeflection coils.

The printing tube 10 has in its face plate a slit 21 along thehorizontal line of the tube. The target member 22 which plays animportant role in this invention is mounted on the outer surface of theface plate, covering the slit 2]. The target 22 is composed of a singlecontinuous dielectric or high resistivity material having a typicalvalue of about 10 ohm-centimeters in resistivity. It is desirable thatthe resistivity of the target material 22 is in a range from about ID toabout 10 ohmcentimeters. These materials are rare. There is nostandardized classification for distinguishing between the dielectricand the semiconducting materials. In a certain classification, thedielectric material is defined as a material of about l to l0ohm-centimeters and the semiconductor material as that of resistivityless than ohm-centimeters. For purposes of this invention, thedielectric material will be defined as a material which may be includedin a range from about 10 to about 10 ohm-centimeters, adding to theabove mentioned range. Charges are deposited only on a portion of thedielectric surface during the time that the target 22 is receivingelectrons from the beam.

Since it is desirable that the charge on the target 22 should disappearas soon as possible after recording is finished, it is advisable toimpart some conductivity to the target 22. These materials with aresistivity of about 10" to 10 ohm-centimeters satisfy this requirementby themselves. However, in case of materials having a resistivity morethan 10 ohm-centimeters, conductivity is insufficient for thisrequirement and thus some conductivity should be added to thesedielectric materials. For example, the inner face of the target 22 ispainted with material having a resistivity of about l0 to 10ohm-centimeters such as chromic oxide including graphite.

. The target 22 has a thickness of approximately I00 microns. Theelectrostatic recording paper 23 is laid at a distance I (microns) fromthe outer surface of the target 22. The electrostatic recording paper 23contains a dielectric sheet 24 which lies on a conducting base 25.Commercially available recording paper can be used for purposes of thisinvention. A gap between the target 22 and the recording paper 23establishes an air layer 26. The gap layer 26 may be swept with adischargeable gas instead of air. A grounding plate 27 always contactsthe conducting base 25 of the electrostatic recording paper 23 and holdsthe potential of the conducting base 25 at the earth potential or nearto the earth potential.

Anode is so grounded as to be held at or near the earth potential.Fourth voltage source 28 is connected between the cathode 11 and theground, so that it impresses from several kilovolts to multiples of l0kilovolts between cathode-toanode.

In this circuit arrangement, no high voltage on the order of kilovoltsis applied to the means of charge pattern deposition which includes theslit 21, the target 22 and the recording paper 23. This differs from theconventional tube for television receiver.

When a high voltage is applied between the cathode 11 and the anode 15,electrons are emitted from the cathode l 1 towards the target 22. On theway to the target 22, the electron beam is first intensity-modulated bythe input signals and then accelerated and focused by electrodes 13 and14. The focused beam is deflected by the deflecting electrodes 20,allowing the beam to scan over the target 22. During the time thatelectrons are emitted from the cathode 11, the target 22 receiveselectrons from the beam and at this time secondary electrons are emittedfrom the target surface because of primary electron impact.

FIG. 2 shows a characteristic curve of secondary-emission ratio N toenergy Ve of electrons which reach the target 22 in the printing tube.The secondary-emission radio N means the average number of secondaryelectrons emitted from a surface per incident primary electron. As canbe seen from this drawing, in the case where the energy Ve of electronsreaching the target 22 is in range from the value VM to the value VN,the ratio N is larger than 1, whereas in case where the energy Ve islarger than the value VN the ratio N is smaller than 1. Therefore, ifthe electron energy Ve is a value e.g. VL smaller than that VN, thesecondary-emission ratio N is larger than 1 and accordingly the innerface of the target 22 is charged positive. And if the electron energy Veis a value larger than the value VN, eg. VH, the inner face of thetarget 22 is charged negative.

In this apparatus the electron energy Ve may be selected at either ofthe values VL and VII. It is better, however, to select the farthestpossible value from 1 as the secondary-emission ratio N and thefollowing will be explained in the case where the value VI-I is selectedfor instance.

The electrons emitted from the cathode ll reach a point over the target22 through the focusing and the deflecting system. Since thesecondary-emission ratio N is smaller than 1, the point over the target22 is charged negative.

FIG. 3 shows an enlarged sectional view of charge deposition mechanismunder the circumstances. An air layer 26 having an interval of t liesbetween the target 22 and the recording paper 23. The charges caused byelectron impact are deposited on only a portion of the inner face of thetarget 22, and are not conducted to the outer face of it. In response tothe charge applied on the target 22, the charged portion shows anegative value of potential. Therefore, it produces the electric fieldsEr, Ea and Ed respectively on the target 22, the air layer 26 and thedielectric sheet 24 of the recording paper 23. As a consequence thereof,the potential difference Va=Ea x t occurs between the recording paper 23and the surface of the target 22 facing the air layer 26. In the casewhere the potential Va reaches a predetermined value, discharge occursin the portion of air layer 26 corresponding to the charged portion ofthe target 22. Negative charge appears in the front of the recordingpaper 23 by this discharge and this negative charge is associated withthe surface of the dielectric sheet 24 of the recording paper 23. It is,therefore, possible to transfer a negative charge image to the recordingpaper 23.

Since the dielectric layer 24 of the recording paper 23 has a highresistivity value, the charge image which is associated with the surfaceof the dielectric sheet 24 does not disappear even though the recordingpaper 23 is kept away from the target 22. Therefore, it is possible toexchange the said charge image for a visible image by using fine coloredelectroscopic powders (toners) with a charge opposite to the said chargeimage. Since a small conductivity is imparted to the target 22, thecharge on the target 22 disappears quickly after recording on therecording paper 23 is finished.

FIG. 4 shows the relation ship between the discharge voltage V and theinterval t. The above discharge voltage V refers to the voltage betweenthe target 22 and the dielectric sheet 24 of the recording paper 23parallel to the target 22. The interval t refers to the distance betweenthe target 22 and the dielectric sheet 24.

If the interval t is small the discharge voltage V is inversely high,and further if the interval 2 is zero or nearly zero the charge patternon the recording paper 23 becomes extremely obscure. In addition, if theinterval 1 is too large the charge pattern becomes blurred. So asuitable interval is required. The inventor has found out by experimentsthat the suitable interval ranges from 5 to 100 microns.

The preferred embodiments are achieved under the following conditions.The control grid voltage is -30 volts, the screen grid voltage is +300volts, the focusing voltage is +1 ,000 volts and the cathode-to-anodevoltage is 17 kilovolts. The grids and focusing voltages are values withrespect to the cathode.

The slit 21 has a width of l millimeter and a length of I80 millimeters.The dielectric target is a glass of the following composition; P 65percent, Fe O 28 percent, A1 0 7.percent. The target is made with aresistivity of ohm-centimeters and a thickness of 150 microns. In therecording paper the dielectric sheet consists of acrylic resin with athickness of 5l0 microns and a resistivity of 10 -10" ohmsentimeters,with a conducting base of a thickness of 65 microns and a resistivity of10 -40 ohm-centimeters. The paper is laid at microns from the surface ofthe target. In joining the target to the face plate, the face plate isfirst painted with low melting point glass powder and then the target ismounted on the face plate. These members are heated at a temperature of450 C for 30 minutes. Copy can be produced at a rate of 7 lines permillimeter in case of a paper running speed of 8.6 millimeters persecond and scanning frequency of 60 Hz.

FIG. 5 shows an enlarged sectional view of an improved charge transportmechanism. The spacer 31 is allowed to contact the outer face of thetarget 22 and it serves to space and protect the target 22. The spacer31 is formed with the target 22 in a body or with the dielectric tapesuch as Mylar tape (trade mark) stuck on the target 22 and thus theinterval 26 is formed. As mentioned above, the value in the range from 5to 100 microns is sufficient for the thickness of the spacer 31 andaccordingly the recording paper 23 faces the target 22 at the requiredinterval allowing the air layer 26 to lie between. Since this printingtube is constructed as mentioned above, there is no direct frictionbetween the thin target 22 and the recording paper 23 thanks to the airlayer 26 between the target 22 and the paper 23, even though therecording paper 23 is allowed to run at high speed, and thus it ispossible to prevent the target from being damaged.

Further if the interval 1 between the spacers 31 on the outer face ofthe target 22 is small, e.g. 0.05 millimeter, it is possible to obtain acharge image of 0.05 millimeter in diameter on the dielectric sheet 24though the diameter of spot of electron beam applied on the target 22 ismore than 0.05 millimeter.

FIG. 6 shows an enlarged sectional view of another improvement. Thespacer 32 is lain between the outer face of the target 22 and therecording paper 23 and further the conducting film 33 is stuck to onesurface of the spacer 32 facing the outer face of the target 22. Thespacer 32 is cut in such a way that one end of it is positioned in thevicinity of the center line of the scanning beam. The conducting film 33is grounded.

In this arrangement creepage discharge takes place along the end face ofthe spacer 32. Therefore, the discharge voltage can be lower than thecase of air discharge. The resolution can be improved because thanks tothe creepage discharge, negative charges, which are produced by thedischarge, collect efficiently at the point of the dielectric sheet 24which contacts the end of the spacer 32. The grounded film 33 causesexcessive charge stored on the outer surface of the target 22 todisappear quickly and thus removes unnecessary charge as a noise.

FIG. 7 shows a printing apparatus for putting the abovementionedprinting tube into use. The printing tube 10 is constructed as mentionedabove and the ground electrode 27 is provided with it being faced to thesurface of the target 22.

The recording paper 23 wound on the supply reel 41 is passed between thesurface of the target 22 and the ground electrode 27 allowing the guiderollers 42, 43, 44 and 45 and taken up at a certain speed by the take-upreel 46. In the travel of the recording paper 23 from the groundelectrode 27 to the v take-up reel 46, a developer 47 allows the toner48 to stick to the recording paper 23. Heater 49 fixes the toner 48which has been allowed to stick to the recording paper 23. As therecording paper 23 coming from the supply reel 41 passes the surface ofthe target 22 with the air layer 26 between, the charge pattern isformed on the surface of the recording paper 23 because of the chargedeposition mechanism. Then a visible pattern is obtained by the toner 48in the developer 47. The developer 47 allows the toner, which has acharge opposite to the charge image on the recording paper 23, to adhereto the charged portion of the recording paper 23 which makes the imagevisible.

Since, however, the developer 47 alone allows the toner 48 to adhere tothe recording paper 23 only insufficiently, the toner 48 is fixedcompletely on the recording paper 23 by the fixing heater 49 andafterwards the recording paper 23 which has finished recording is takenup by the take-up reel 46.

FIG. 8 shows a variation of FIG. 7. An endless recording tape 51 whichhas a dielectric sheet or a photo-conductive layer such as seleniumformed on the substrate of relatively low resistivity is passed betweenthe printing tube 10 and the ground electrode 27. It is driven in thedirection of the arrow at a given speed over guide rollers 52, 53, 54,55 and the grounded guide 56.

A belt conveyor 57 is driven in the direction of the arrow by thedriving wheels 58, 59 and allows the toner 60 to flow consecutively overthe portion of the recording tape 51 positioned between the guiderollers 53 and 54. Facing the grounded guide 56, is a corona dischargegenerator 60. The recording paper 61 unwound from the supply reel 62 isallowed to contact the tape 51 between the guide rollers 63 and 64 andis taken up at the same speed as the running speed of the tape 51 by thetake-up reel 65. As shown in FIG. 7, a fixing heater 66 is also providedin the course of travel of the recording paper 61 between the guideroller 64 and the take-up reel 65. In the travel of the tape 51 past theguide 56 a remover 67 is provided. The tape 51 is moved over the surfaceof the target 22 and the air layer 26 where a charge image is formed onthe face of the tape 51. The toner 60 conveyed by the belt conveyor 57adheres to the portion of the recording tape 51 having the chargepattern and thus visible a image is obtained. The toner 60 which has notadhered to the recording tape 51 drops as it is and is conveyed again bythe conveyor 57.

The portion of the tape 51 which has a visible image produced the toner60 contacts the recording paper 61 at the guide 56 which moves at thesame speed. At the same time, a corona discharge generator 60 causescorona discharge, and the charge obtained by this phenomenon is impartedto the rear side of the recording paper 61 (the discharge generatorside).

As a result, the toner which has adhered to the recording tape 51 istranscribed on the surface of the recording paper 61 and thus the imageis produced. The fixing heater 66 causes the toner on the recordingpaper 61 to be fixed permanently.

Any toner adhering to the recording tape 51 and also charge is removedcompletely by remover 67, and the tape 51 reaches the surface of thetarget 22 again.

If a photo-conductive sheet such as selenium is employed as the abovetape 51, the whole apparatus should be shielded from light. However, theportion after the charge image is removed by the remover 67 may beexposed to light.

In addition, it is possible to record a different optical image over thecharge image through the optical system 68.

I claim:

1. An electrostatic printing apparatus comprising: a cathode ray tubecontaining an electron gun, an electron scanning means and a continuoustarget member which is composed of a single dielectric material saidtarget having a resistivity in a range from about 10" to about 10ohm-centimeters, the continuous target being scanned by electrons fromthe electron gun so that charge is deposited only on a portion of thetarget where the electron beam strikes, a dielectric recording sheettraveling in front of the continuous target, and a gaseous gap layerbetween the continuous target and the recording sheet through which thecharge patterns on the continuous target are transferred to therecording sheet by means of discharge.

2. An electrostatic printing apparatus according to claim 1 whichcomprises means of developing the charge patterns on the recording sheetwith toner and means of fixing the toner on the recording sheet.

3. An electrostatic printing apparatus comprising: a cathode ray tubecontaining an electron gun, an electron scanning means and a continuoustarget member which is composed of a single dielectric material asurface of the dielectric target being painted with materials having aresistivity of about 10 l0 ohm-centimeters, the continuous target beingscanned by electrons from the electron gun so that charge is depositedonly on a portion of the target where the electron beam strikes, adielectric recording sheet traveling in front of the continuous target,and a gaseous gap layer between the continuous target and the recordingsheet through which the charge patterns on the continuous target aretransferred to the recording sheet by means of discharge.

4. An electrostatic printing apparatus comprising: a cathode ray tubecontaining an electron gun, an electron scanning means and a continuoustarget member which is composed of a single dielectric material, thecontinuous target being scanned by electrons from the electron gun sothat charge is deposited only on a portion of the target where theelectron beam strikes, a dielectric recording sheet traveling in frontof the continuous target, a gaseous gap layer between the continuoustarget and the recording sheet through which the charge patterns on thecontinuous target are transferred to the recording sheet by means ofdischarge and a spacer laid between the surface of the target and thedielectric recording sheet.

5. An electrostatic printing apparatus according to claim 4 whichcomprises a conducting film being laid between the surface of the targetand the spacer.

6. An electrostatic printing apparatus according to claim 5 in which thespacer is cut in such a way that one end of the spacer is positioned inthe vicinity of the center line of the scanning beam, thus allowingcreepage discharge to occur along the end face of the spacer.

1. An electrostatic printing apparatus comprising: a cathode ray tubecontaining an electron gun, an electron scanning means and a continuoustarget member which is composed of a single dielectric material saidtarget having a resistivity in a range from about 107 to about 1012ohm-centimeters, the continuous target being scanned by electrons fromthe electron gun so that charge is deposited only on a portion of thetarget where the electron beam strikes, a dielectric recording sheettraveling in front of the continuous target, and a gaseous gap layerbetween the continuous target and the recording sheet through which thecharge patterns on the continuous target are transferred to therecording sheet by means of discharge.
 2. An electrostatic printingapparatus according to claim 1 which comprises means of developing thecharge patterns on the recording sheet with toner and means of fixingthe toner on the recording sheet.
 3. An electrostatic printing apparatuscomprising: a cathode ray tube containing an electron gun, an electronscanning means and a continuous target member which is composed of asingle dielectric material a surface of the dielectric target beingpainted with materials having a resistivity of about 107 - 1012ohm-centimeters, the continuous target being scanned by electrons fromthe electron gun so that charge is deposited only on a portion of thetarget where the electron beam strikes, a dielectric recording sheettraveling in front of the continuous target, and a gaseous gap layerbetween the continuous target and the recording sheet through which thecharge patterns on the continuous target are transferred to therecording sheet by means of discharge.
 4. An electrostatic printingapparatus comprising: a cathode ray tube containing an electron gun, anelectron scanning means and a continuous target member which is composedof a single dielectric material, the continUous target being scanned byelectrons from the electron gun so that charge is deposited only on aportion of the target where the electron beam strikes, a dielectricrecording sheet traveling in front of the continuous target, a gaseousgap layer between the continuous target and the recording sheet throughwhich the charge patterns on the continuous target are transferred tothe recording sheet by means of discharge and a spacer laid between thesurface of the target and the dielectric recording sheet.
 5. Anelectrostatic printing apparatus according to claim 4 which comprises aconducting film being laid between the surface of the target and thespacer.
 6. An electrostatic printing apparatus according to claim 5 inwhich the spacer is cut in such a way that one end of the spacer ispositioned in the vicinity of the center line of the scanning beam, thusallowing creepage discharge to occur along the end face of the spacer.